While researching at a busy bar, scientists found that nine out of 10 customers were most successful using this subtle technique.

Less than one in 25 were successful by shouting or waving at the bartender.

“Effectively, the customers identify themselves as ordering and non-ordering people through their behavior," said study author Sebastian Loth, of Bielefeld University.

“Two signals are necessary and together form the sufficient set of signals for identifying the intention to place an order. First, the customers position themselves directly at the bar and, secondly, look at the bar/bartender."

The goal of the research? To help design a robot to serve drinks most efficiently and effectively.